1. Field of the Invention
Aspects of the present invention relate to a thin film transistor, and more particularly, to a thin film transistor including a semiconductor layer fabricated so as not to include, especially in a channel region, a seed or a grain boundary created in the crystallization of an amorphous silicon layer into a polycrystalline silicon layer by use of a super grain silicon (SGS) crystallization method.
2. Description of the Related Art
Recently, flat panel displays, such as, for example, liquid crystal display devices, organic electroluminescent devices and plasma display panels (PDPs), which overcome the disadvantages of heavy, large conventional display devices such as cathode ray tubes, have been receiving a lot of attention.
Among the elements that make up a flat panel display device, a thin film transistor has a notably significant effect on the properties of the device. In particular, the properties of the semiconductor layer in the thin film transistor directly affect the properties of the flat panel display.
The properties of the thin film transistor are dependent upon properties of the semiconductor layer, and generally, the properties of the semiconductor layer improve when its crystallinity improves.
In general, methods of crystallizing an amorphous silicon layer into a polycrystalline silicon layer include solid phase crystallization (SPC), excimer laser crystallization (ELC), metal induced crystallization (MIC), and metal induced lateral crystallization (MILC). SPC is a method of annealing an amorphous silicon layer for several hours at a temperature of 700° C. or less, at a transition temperature of glass. SPC is typically used to form the substrate of a display device that uses a thin film transistor. ELC is a method of crystallizing a silicon layer by irradiating it with an excimer laser and locally heating it to a high temperature for very short time. MIC is a method of using phase transfer induction to convert an amorphous silicon layer to polysilicon by contacting the amorphous silicon layer with a metal such as Ni, Pd, Au and Al or by implanting such a metal into the amorphous silicon layer. MILC is a technique of inducing sequential crystallization of silicon by lateral diffusion of silicide formed by reacting metal with the silicon.
However, SPC not only takes a long time, but also produces an inferior crystal. ELC requires an expensive apparatus, and MIC and MILC result in a large leakage current due to catalysts remaining in the silicon.